Method and apparatus for accelerating ions of any mass



June 27, 1967 B. 1-1. SMITH ETAL 3,328,708

METHOD AND APPARATUS FOR ACCELERATING IONS OF ANY MASS Filed March 4,1965 2 Sheetssheet 1 1 SYNCHROTRON 62 MAGNET POWER SUPPLY a [4 If 12-1/13-2 STORAGE RING 24 MAGNET POWER /63 14 SUPPLY 22 I36/ RADIO FREQUENCYSYSTEM INVENTORS 3 BOB H. 311111111 FREQUENCY /64 ROBERT M. MAIN CONTROLALBERT GH/ORSO ma-W ATTORNEY June 9 B. H. SMITH ETAL 3,323,703

METHOD AND APPARATUS FOR ACCELERATING IONS OF ANY MASS Filed March 4,1965 2 Sheets-Sheet 2 INVENTORS 808 H. SMITH ROBERT M. MAIN ALBERTGHIORSO ATTORNEY United States Patent 3,328,708 METHOD AND APPARATUS FORACCELERATING IONS OF ANY MASS Bob H. Smith, Berkeley, Robert M. Main,Oakland, and Albert Ghiorso, Berkeley, Caliii, assignors to the UnitedStates of America as represented by the United States Atomic EnergyCommission Filed Mar. 4, 1965, Ser. No. 437,332 16 Claims. (Cl. 328-235)This invention relates to the acceleration of charged particles to highenergies in synchrotrons and more particularly to a method and apparatusfor accelerating particles having very different masses includingparticles which are much heavier than those heretofore accelerated bysuch means. The invention provides techniques for producing a beam ofions of any desired element within a synchrotron.

It is increasingly evident that beams of high energy heavy particleshave particular physical properties which are of great interest in manynew fields of biological inquiry at virtually every level. Theinteraction of heavy particles with biological tissue is related to thehighlinear-energy-transfer properties of the heavy particles. With ahigh-linear-energy-transfer, a quantitatively differentmode of bothexcitation and ionization seems to occur in matter; as a result it isfound that the effects of heavy particles on crystals, organicmolecules, proteins, and living cells involve different molecularmechanisms than do the effects of lightly ionizing rays.

It has become apparent, for example, that the production of high energybeams of heavier ions will be of very great interest in connection withcancer research. Studies at existing accelerators have shown that such abeam can be used to irradiate an aifected region with little deleteriouseffect on the healthy tissue through which the beam must pass to reachthe affected region, owing to the Bragg peak. Lesions without scarringmay be produced in a laminar plane by a penetrating sheath of heavyparticles, the lesion running parallel to the surface of the tissue at apredetermined depth. The availability of a source of heavy ions is alsoof great importance to many other phases of basic bio-medical researchand in space medicine studies.

Heavy ions can be accelerated by many of the various conventional typesof particle accelerator, however, each has certain disadvantages whenused for this purpose. For instance, with electrostatic acceleratorssuch as the Cockcroft-Walton type, the maximum obtainable energy isseverely limited. To a lesser degree, the maximum practical energy whichcan be obtained for heavy ions in a cyclotron is also limited. A linearaccelerator can be used to obtain a high energy for a particular heavyparticle, but for all lighter particles of similar charge the maximumattainable energy from a specific linear accelerator is correspondinglyless. Thus the weight range of particles which may be effectivelyaccelerated in a given linear accelerator is very limited. Also, theextreme length, and therefore the cost, of a linear accelerator for theheavier particles is a practical obstacle to the use of such means. Alinear accelerator is ordinarily utilized to inject particles into asynchrotron and therefore the limitations of the linear accelerator areimposed upon the synchrotron. If heavy particles are injected into asynchrotron from a cyclotron, the cost is again very great; while ifheavy particles are injected into a conventionally operated synchrotronfrom an electrostatic generator, the maximum obtainable output energy islimited by the low injection energy.

In the present invention a synchrotron is utilized in a novel manner toovercome the above-mentioned difficulties. The synchrotron as employedin the present inven- "ice tion is conventional insofar as ions areaccelerated to a higher speed during each revolution around thesynchrotron by a radio-frequency potential, the frequency of which isincreased in step with the increase in the energy of the acceleratedparticles. In each stage of particle acceleration, the magnetic fieldintensity of the synchrotron is swept from a minimum to a maximum sothat the ions remain in an orbit of nearly constant radius.

In this invention, particles are injected into the synchrotron by anelectrostatic accelerator. Ordinarily, atoms of an element of highatomic weight can only be initially ionized to a relatively loWcharge-to-mass ratio, i.e., only a few of the orbital electrons can beremoved. Any ion will be accelerated by an electrostatic accelerator,but the amount of acceleration is proportional to the chargeto-massratio. Thus, the heavier nuclei such as uranium, for example, which areinitially ionized with a very low charge-to-mass ratio, must necessarilybe injected into the synchrotron at a relatively low velocity.

While the charge-to-mass ratio of the ions can be raised by passing theions through an electron stripper such as a thin metallic foil, suchstripping can be satisfactorily accomplished only after the ions havebeen accelerated to a much higher velocity than is obtainable in theelectrostatic injector accelerator. However, as mentioned previously,the maximum energy which may be imparted to the ions in a singleacceleration stage of a synchrotron is limited by the charge-to-massratio of the particle and by the maximum magnetic field obtainable.

Thus the basic problem in connection with accelerating heavier ions in asynchrotron is that the ions cannot, initially be given the degree ofcharge that would be required to allow the synchrotron to accelerate theions to the desired high energy. While the ions can be given the neededhigh charge by stripping, after some acceleration in the synchrotron,the magnetic field thereof cannot be abruptly changed in the middle of acycle to adjust to a sudden radical change in the charge of ions whichare circulating therein.

To overcome these problems, in the present invention, ions of relativelyloW charge are accelerated to the maximum velocity obtainable in asingle cycle and then are extracted from the synchrotron. The ions arethen passed through an electron stripper wherein several or all theremaining orbital electrons are removed. These stripped highly chargedions are then injected into a storage ring. While the magnetic field ofthe synchrotron is being decreased back to a minimum value inpreparation for a second stage of acceleration, the ions circulate inthe storage ring in a steady state magnetic field. At the beginning ofthe next synchrotron cycle the ions are then re-injected into thesynchrotron and, taking advantage of the higher charge-to-mass ratioobtained by removal of electrons in the stripper, the ions are furtheraccelerated to a very high energy. Alterna-tely, the ions may be storedin the initial charge state and stripped just prior to re-injection intothe synchrotron. After the second stage of acceleration, the ions may beextracted and used to bombard a target; or may be further stripped ofelectrons, stored, re-injected into the synchrotron and acceleratedstill more in a third stage of acceleration.

This accelerator system has been designated as an Oinnitron in view ofits capability of accelerating ions of any atomic weight to all energieswithin the minimum and maximum design range.

It is an object of this invention to increase the versatility of chargedparticle accelerating installations.

It is an object of the present invention to provide a method andapparatus suitable for accelerating particles of any atomic weight tohigh energies.

It is another object of the present invention to provide techniques bywhich the peak output energy of ions from accelerators of thesynchrotron type can be efilciently increased.

It is another object of the present invention to provide a method andapparatus for accelerating heavy ions in a synchrotron from a lowinitial injection energy to a very high output energy.

It is another object of the invention to provide a highly versatilesynchrotron system having a very low energy spread obtainable over awide, continuously variable energy range.

it is still another object of the invention to provide for therepetitive staged acceleration of ions to successively higher energieswithin a single accelerator of the synchrotron class.

It is a further object of the invention to facilitate the study andtreatment of biological conditions by providing for the generation ofhigh energy beams of a wide variety of heavy charged particles.

The invention will be better understood by reference to the accompanyingdrawing of which:

FIGURE 1 is a diagrammatic plan view of a synchrotron storage ring andappurtenances in accordance with the invention,

FIGURE 2 is an enlarged more detailed view of the segment of thesynchrotron of FIGURE 1 which is enclosed by dashed line 2 thereon, and

FIGURE 3 is a greatly enlarged and more detailed cross-sectional viewtaken at line 33 on FIGURE 2 and showing the magnet and gap structure ofthe synchrotron.

Referring now to FIGURE 1 there is shown a synchrotron 11 having eightmajor beam-guiding magnet sectors 12 for containing and directing theion beam in an annular orbit, the sections being separated by eightorbit straight sections 13. In order to refer separately to individualstraight sections 13 and curved magnet sections 12, the referencenumbers will be followed by a number designating an individual sector orsection, proceeding clockwise around the synchrotron, for example 131 to13-8 for the straight sections. Four conventional radio-frequencyaccelerating resonators 14 are provided in alternate straight sections13-2, 13-4, 13-6 and 138, while various pulsed beam-bending magnets aredisposed in the remaining straight sections for receiving and extractingan ion beam as will be described later. Except as will be hereindescribed, the structural detail and components of the synchrotron 11may be of customary design as understood by those skilled in the art.

The ions are first created and formed in a low energy beam in aCockcroft-Walton accelerator 16 or the like and directed into a beaminfiector 17 at one of the straight sections 134.7, which guides theions into the synchrotron beam orbit. The beam then circulates through along annular vacuum pipe 15 Which extends around the synchrotron andencloses the beam orbit thereof. In FIGURE 1, arrows are provided alongvacuum pipe 15 to indicate the direction of the ion beam.

A constant orbit radius is maintained inasmuch as the ions areaccelerated concurrently with the increase in magnetic field intensity.When the maximum available magnetic field is obtained and the particlereaches maximum energy, the ion beam is extracted inwardly by a beamextractor 31 at one of the straight sections 135 and is guided through aseries of beam-bending magnets 18 and 19. The resonators 14 areenergized from one or more conventional synchrotron radio-frequencysystems 61 while the synchrotron and storage ring magnets are energizedfrom direct current power supplies 62 and 63. A frequency control 64- isoperated as in a conventional synchrotron, the control correlating thefrequency provided by the radio-frequency systems 61 with the magneticfield intensity so that the path of the charged particles in thesynchrotron is maintained near the center of the vacuum pipe 15. Suchcontrol also provides for synchronizing and correlating the operation ofthe various elements of the omnitron as will be described.

An electron stripper foil 24 is disposed between the bending magnets 13and 19 to increase the charge on the ions after extraction from thesynchrotron 11. Foil 24- removes one or more electrons from the ions,the number removed depending mainly upon atomic number and velocity ofthe ion, and to some extent upon foil thickness.

A beam storage ring 21 is disposed within the area enclosed bysynchrotron 11 and is comprised of four curved beam-guiding magnetsections 22 mutually separated by four straight sections 23. Theaccelerated ion beam from synchrotron 11 is directed into the storagering 21 at one of the straight sections 234 thereof at a beam inflector32. The magnetic field intensity in the beam guide magnet sections 22 ofstorage ring 21 is steady state and the ion beam circulates around thestorage ring without change in energy. In the meantime, the magneticfields in the synchrotron guide magnets 12 are recycled to the necessarylow value for re-injection of the stored particles into the synchrotron11. The stored ion beam is then extracted from the storage ring 21 bythe beam extractor 33 at one of the straight sections 23-1 thereof, theions being guided by two beam-bending magnets 26 and 27 for re-entryinto the synchrotron 11 by beam inflector 34 at one of the straightsections 13-3.

The ion beam is then again accelerated in the synchrotron 11 as before,however, since the injection velocity of the ions is much higher than inthe first acceleration state, a higher harmonic of the radio-frequencysignal is utilized for accelerating the ions, as discussed later.

After the second cycle of acceleration of the ions in synchrotron 11,the ion beam can again be directed back through the stripper foil 24 tothe storage ring 21, in preparation for a third acceleration.Ultimately, however, the ions are extracted from either the storage ring21 or syn chrotron 11 for bombarding a target, for the treatment of amedical patient, or for any of the other uses for which charged particlebeams are employed.

If a well-defined brief pulse of ions is to bombard a target 28, theion, beam can be extracted at straight section 13-1 by beam extractor 36of synchrontron 11 and directed toward the target. If, on the otherhand, the ions are to strike an alternate target 29 at a more constantrate over an extended time interval, then the beam may be extracted fromthe storage ring 21 by beam extractor 37 at straight section 232 anddirected to the target.

More details of the synchrotron structure are shown in FIGURE 2, whichis an enlarged view of straight section 135 with the adjoining potrionsof guide magnet sectors 125 and 12-6. Many individual guide magentsections 41 form each magent sector 12, a greatly enlarged cross-sectionview of the structure of magnet sections 41 being shown in FIGURE 3.Subjacent each magnet section 41 is an adjustable positioning means 42,disposed on a concrete foundation 43, which is provided to facilitatethe alignment of each guide magnet 41. Each such magnet section furtherincludes a C-shaped iron core 44 with pole tips 46 suitably shaped toprovide an alternating gradient field, as described in detail inPhysical Review 88, 1190 (1952), by Courant et al. The vacuum pipe 15through which the ions pass extends between the pole tips 4-6. Thebeam-guiding magnetic field is produced by magnet coils 48 and 49disposed around each of the pole tips 46.

With reference again to FIGURE 2, each major sector 12 of thesynchrotron magnet is comprised of many of the magnet sections 41disposed along the beam orbit 15 with successive ones of the sectionsfacing in opposite directions to produce the alternating gradienteffect. To correct any tendency of the ions to deviate widely from theoptimum orbit, supplementary focussing means are disposed at intervalstherearound. Thus in the straight section 135 the ion beam orbit passesthrough two conventional quadrupole magnetic focussing lenses 51 and 52.In the beam extractor 31, a pair of ferrite core pulsed magnets 53 and54 for deflecting the ion beam out of the synchrotron are disposed inthe straight section 135.

The straight sections 131, 13-3 and 13-7 of synchrotron 1'1 utilizeother beam extracting or beam inflecting means 36, 34 and 17 similar tothat described with respect to FIGURES 2 and 3.

The magnet sectors 22 and the straight sections 23 of the storage ring21 may have a detailed construction essentially similar to that of thesynchrotron-11 as described with reference to FIGURES 2 and 3.

While the design of an accelerator system for practicing the presentinvention may be varied in very many respects, an example ofspecifications for a particular embodiment of the invention is asfollows:

Injection system Cockcroft-Walton injection potential rnegavolts 2Synchrotron 11 6 Energy (a) Greater than 400 million electron-volts(mev.) per nucleon for all ions having an atomic weight equal or lessthan 40 (b) Greater than 300 million electron volts (mev.) per nucleonfor all ions having an atom weight equal to or less than 238 (Uranium)(c) Energy spread does not exceed 0.2%.

Beam intensity (a) Number of alpha particles should be greater than 4 10particles per second at 100-400 mev. per'nucleon (b) Number of xenonparticles should be greater than 1'10 particles per second up to 15 mev.per nucleon.

This synchrotron provides 60 acceleration stages per second. Therefore,if two-stage acceleration is used, the beam output rate is 30 pulses persecond.

Ions are created with only the outer few electrons removed. Withprogressively heavier nuclei, the e/m (charge-to-mass) ratio of ionsavailable in quantity from existing ion sources decreases. For uranium,for example, it is only 0.02. Acceleration by the Cockcroft-Walter in-Magnet: 25 jector 16 is proportional to the charge-to-mass ratio so I I2 Mean 0rb1t diameter feet 93 the amount of acceleration of the heavierions decreases Maximum guide field kilogauss 10 with increasing massnumber. The relatively slow speed Useful aperture inches 1% x 2% ofthese particles requires a very low orbit frequency in Number of magnets64 the synchrotron at injection, the orbit frequency being Length ofmagnets inches 28 30 defined as the reciprocal of the orbit periodaround the Number of straight sections 8 accelerator. Length of straightsections feet 12 In Table I there is shown a tabulation of orbitfrequen- Weight of steel tons 77 cies, harmonic numbers andradio-frequency data. The. Weight of copper do 13 harmonic number may bedefined as the number of radio- Stored energy kilojoules 212 frequencycycles occurring at a particular resonator 14 Input power, ACkilowatts.. 134 forone revolution around the synchrotron of a particularInput power, DC do 268 particle.

TABLE I Orbit freq. (megacycles) Orbit period (500.) Freq.ofRF(megacycles) Elm Harmgnie V Max Min. Min. Max. Hum er Max. Min.

Accelerqfion system Thus as indicated above, for particles withe/m==0.02, Maximum frequency mc /Sec 33 the orbit frequently is only0.0311814 mc., while the Minimum frequency 1 6 highest orbit frequency(corresponding to lighter particles Energy gain per tum 'i with em=0.5)is 2.556498 me. The ratio of these freeg of gg kg n u 4 quencies is82/1. If the radio-frequency system of the synchrotron had to cover thisrange, the task would be Storage ring 21 6 formidable. However, if theharmonic number is varied Mean orbit diameter feet 54 inversely with thec/m ratio, the dynamics of the syn- Guide field 'ig g 10 chrotron areindependent of e/m, thus the frequency Useful apertur; l 1 2% range isessentially constant for all particles, and the neces- Number of g u 40sary range of the radio-frequency system is approxi- Length of magnetsinches 28 ii Number of Straight Sections 4 e pm 16m of qq l h phaserelatwnshlp 3 Length of Strainht Sections feet 12 tween the severalcavlties 1s cons1derably reduced by dr1v- Wei ht of steel 48 ing all theradio-frequency resonators 14 in-phase and Weight of Co 8 selecting onlyharmonic numbers which are integrals of Inpugt power Pp ig g 370 thenumber of resonators. For an accelerator with the above-describedconfiguration, a radio-frequency system covering the range from 1.6 to33 mc. is required. This frequency range can be accommodated byincluding two cavities in each of the resonators 1 4. The first cavitytunes from 1.6-to 7.5 mc., the second from 7 to 33 me. The

portion of the available frequency range actually utilized in anyparticular acceleraing stage depends upon the e/m ratio of theparticular ions being accelerated. Such a system is described in detailin the report, The RF System for Princeton-Penn Accelerator, PrincetonUniversity Report PPAD408E, 1961, by J. Reidel et .al.

The number of bunches of particles in a synchrotron is equal to theharmonic number of the radio-frequency. For uranium with an e/m ratio of0.02 there are 192 bunches, each spaced only 18 inches apart. For lowerharmonic numbers the bunch spacing increases.

At full field the transit time of the particles around the describedsynchrotron orbit varies from 6.4 microseconds for e/m=0.02, to 0.391microseconds for e/m=0.5 particles. Because of the choice of harmonicnumber, the time between particle bunches is approximately the same forall beams0.030 microseconds.

Obviously, many variations may be made in the design of the invention,for instance; the storage ring 21 is not necessarily disposed within thesynchrotron, the number of straight sections may be altered; andelectrostatic beam inflection and extraction may be utilized rather thanthe magnetic components as herein described, suitable detailedstructures for either type being known to those skilled in the art.

Therefore, while the invention has been disclosed with respect to aspecific embodiment, it will be apparent to those skilled in the artthat numerous variations and modifications may be made within the spiritand scope of the invention and it is not intended to limit the inventionexcept as defined in the following claims.

What is claimed is:

1. In a method for producing high energy beams of heavy ions in asynchrotron, which synchrotron is of the class having a cyclicallyvarying magnetic field defining a particle orbit and a cyclicallyvarying electrical field thereat for accelerating ions therearound, thesteps comprising generating said ions with a first charge-to-mass ratio,accelerating said ions at said orbit of said synchrotron to a firstenergy level during a first cycle of said magnetic field thereof,raising the charge-to-mass ratio of said ions to a second higher value,and further accelerating said ions at said orbit in said synchrotron toa second higher energy level during a subsequent cycle of said magenticfield, said further acceleration of said ions being phased with a higherharmonic of said electrical field than the initial acceleration thereof.

2. A method for producing high energy beams of heavy ions as describedin claim 1 and comprising the further step of changing the frequencyrange of said electrical field between the initial acceleration of saidions and the further acceleration thereof to compensate for the changedcharge and energy of said ions.

3. A method for producing a high energy beam of particles in asynchrotron comprising the steps of initially ionizing said particles toa low charge-to-rnass ratio, accelerating said particles in saidsynchrotron during a first operating cycle thereof, storing theaccelerated particles outside said synchrotron, raising thecharge-to-mass ratio of said particles during the storage period, andfurther accelerating said particles in said synchrotron during asubsequent operating cycle thereof.

4-. A period for imparting high energy to atomic nuclei which may be ofany atomic weight comprising the steps of removing a portion of theorbital electrons from said nuclei, injecting said nuclei into a chargedparticle accelerator at the start of a first acceleration stage thereof,removing said nuclei from said accelerator at the end of said firstacceleration stage, storing said nuclei until the start of a subsequentacceleration stage of said accelerator, removing additional orbitalelectrons from said nuclei following said first acceleration stage, andre-injecting said nuclei into said accelerator at the start of asubsequent acceleration stage for further acceleration therein.

5. A method for producing a high energy beam of multiply chargedpraticles from atoms which may be of any atomic weight in a synchrotronof the class having a cyclical magnetic field defining a particle orbitand a cyclical frequency modulated electrical field thereat foraccelerating ions therearound, comprising the steps of removing aportion of the orbital electrons from said atoms to produce ions,injecting said ions into said synchrotron, accelerating said ions insaid synchrotron during a first cycle of said magnetic field, removingsaid accelerated ions from said synchrotron and storing said ions untila subsequent cycle of said magnetic field and a subsequent sweep of saidfrequency modulated electrical field, stripping additional orbitalelectrons from said ions during the interval between accelerating stagesto increase the charge thereof, re-injecting said ions into said orbitof said synchrotron, and further accelerating said ions during saidsubsequent cycle of said magnetic field in phase with a higher harmonicof said electrical field.

6. In apparatus for generating high energy ion beams, the combinationcomprising a charged particle accelerator, an ion source coupled theretofor injecting ions into said accelerator at a first charge-to-mass ratiowhereby said ions are accelerated to a first energy level, an ion beamstorage device, an ion extractor connecting said accelerator with saidstorage device whereby said ions may be transformed thereto followingacceleration to said first energy level, means connecting said storagedevice with said accelerator for returning said ions thereto followingstorage for further acceleration therein, and an ion stripping elementdisposed in the path of said ions between said accelerator and saidstorage device whereby the charge-to-mass ratio of said ions is raisedto a second higher value prior to said further acceleration thereof.

7. In apparatus for accelerating multiply charged ions to high energies,the combination comprising a charged particle accelerator of the classhaving a cyclical magnetic field defining an ion orbit and having acyclical frequency modulated electrical field thereat for acceleratingions therearound, an ion source coupled to said accelerator forinjecting ions having a first charge-to-mass ratio into said orbit foracceleration during a first cycle of said magnetic field of saidaccelerator, an ion beam storage ring of the class having a magneticfield defining an ion beam orbit, first beam guiding means connectingsaid accelerator orbit and said storage ring orbit for transferring saidions to said storage ring following said first cycle of acceleration,second beam guiding means connecting said storage ring orbit and saidaccelerator orbit for returning said ions thereto during a secondsubsequent cycle of said magnetic field of said accelerator for furtheracceleration thereby, and an ion stripping element disposed in the pathof said ions between said accelerator orbit and said storage ring orbitfor raising the charge-to-mass ratio of said ions to a second highervalue prior to said further acceleration.

8. In apparatus for accelerating multiply charged ions to high energiesas described in claim 7, the further combination comprising a frequencycontrol circuit coupled to said accelerator for changing the frequencyrange of said electrical field thereof between the first and sec ondacceleration periods of said ions to adjust for change in charge-to-massratio and changed energy thereof.

9. In apparatus for accelerating multiply charged ions to high energiesas described in claim 7, the further combination comprising a controlcircuit coupled to said accelerator, said ion source and said first andsecond beam guiding means and sequentially activating said source andsaid first and second beam guiding means in a predetermined timedrelationship with respect to the magnetic field cycle of saidaccelerator.

10. In apparatus for bombarding a target with charged particles, thecombination comprising a source of said charged particles, a synchrotronof the class having a cyclically varying magnetic field forming a closedparticle orbit and having a cyclically varying frequency modula-tedelectrical field thereat for accelerating successive pulses of saidparticles, a charged particle beam storage ring, a first particleinjector coupling said source to said synchrotron for injecting saidcharged particles from said source into said orbit of said synchrotronduring a first acceleration cycle thereof, a first particle extractordisposed at said synchrotron orbit to remove said charged particles fromsaid synchrotron following said initial acceleration thereof, a secondparticle injector disposed at said storage ring and coupled to saidfirst extractor for receiving said charged particles from said firstextractor and adapted to inject said particles into said storage ring, asecond particle extractor disposed at said storage ring and adapted toremove said charged particles from said storage ring during a secondsubsequent acceleration cycle of said synchrotron, a third particleinjector disposed =at said synchrotron and coupled to said secondparticle extractor for receiving said charged particles from said secondextractor and adapted to re-inject said particles into said synchrotronfor a further stage of acceleration, an electron stripper disposed inthe path of said charged particles between said synchrotron orbit andsaid storage ring to increase the charge of said particles between saidacceleration stages, and means for directing said charged particles fromsaid synchrotron to said target following said further accelerationthereof.

11. Apparatus for bombarding a target with charged particles asdescribed in claim 10, wherein said synchrotron is provided with acircuit controlling the frequency of said electrical field, said circuitproducing a high frequency charged particle accelerating potentialvariable over a range of frequencies, the frequency of said acceleratingpotential having a harmonic the number of which is equal to the numberof high frequency cycles through which said electrical field passesduring the time required for said charged particles to complete onerevolution around said synchrotron, said harmonic number being of aprogressively lower order during successive ones .of said accelerationstages.

12. In apparatus for bombarding a target with heavy ions which may be ofany selected atomic weight, the combination comprising an ion source, anelectrostatic accelerator coupled thereto for accelerating said ionsfrom said source, a synchrotron having an ion input coupled to saidelectrostatic accelerator for receiving said ions from saidelectrostatic accelerator, said synchrotron having a beam guiding magnetstructure defining a closed orbit with a field capable of being variedacross a range of intensities, said synchrotron having resonators spacedaround said orbit accelerating ions, said synchrotron further havingradio-frequency power producing means coupled to said resonators, afirst extractor at said orbit for removing said ions from saidsynchrotron, a storage ring receiving said ions from said firstextractor, a second extractor for removing said ions from said storagering and re-directing said ions into said synchrotron orbit, meansdisposed in the path of said ions and outside said synchrotron orbit forstripping additional electrons from said ions between successiveacceleration stages, a control circuit in said synchrotron correlating afirst selected harmonic of the frequency of said radio-frequency powerwith the intensity of said magnetic field whereby said ions aremaintained in said orbit, said control circuit being adapted tocorrelate a second selected harmonic of said radio-frequency power withmagnetic fieldintensity for maintaining an orbit of fixed radius forsaid ions that are returned to said synchrotron orbit from said storagering, said second selected harmonic being of a lower order than saidfirst selected harmonic, and a third extractor disposed at saidsynchrotron orbit for directing said ions from said synchrotron to saidtarget.

13. Apparatus for bombarding a target with heavy ions as described inclaim 12, wherein said electrostatic accelerator is of theCockcroft-Walton type.

14. Apparatus for bombarding a target with heavy ions as described inclaim 12, wherein said stripping means is a thin sheet of metallic foildisposed transversely in the path of said ions between said firstextractor and said storage ring.

15. Apparatus for accelerating heavy ions comprising an ion source, anelectrostatic accelerator coupled to said source and accelerating ionstherefrom, a synchrotron having an ion input connected to saidelectrostatic accelerator for further accelerating said ions, saidsynchrotron further having a plurality of curved spaced-apart magnetsectors forming a closed ion orbit in which a plurality of straightorbit sections separate adjacent pairs of curved orbits sectors, an ionbeam storage ring having a plurality of curved spaced-apart magnetsectors each separated by straight sections, a first ion extractordisposed at a first of said stratight sections in said synchrotronorbit, =a first ion injector disposed at a firs-t straight section insaid storage ring positions to receive ions from said first extraction,an electron stripping foil disposed in the path of said accelerated ionsbetween said first straight section of said synchrotron and said firststraight section of said storage ring, a second ion extractor disposedat said storage ring for removing stored ions from a second straightsection of said storage ring, a second ion injector disposed at saidsynchrotron and positioned to receive ions from said second extractorfor re-injection into a second straight section of said synchrotron, andmeans disposed at said synchrotron for directing fully accelerated ionsto a target.

16. Apparatus for accelerating heavy ions as described in claim 15,further characterized in that said storage ring is disposed within saidsynchrotron.

References Cited UNITED STATES PATENTS 2,473,477 '6/ 1949 Smith 313622,789,221 4/ 1957 Tobias 328--233 3,227,597 1/1966 Feldm-ann 328234JAMES W. LAWRENCE, Primary Examiner.

V. LA FRANCHI, Assistant Examiner,

1. IN A METHOD FOR PRODUCING HIGH ENERGY BEAMS OF HEAVY IONS IN ASYNCHROTON, WHICH SYNCHROTON IS OF A CLASS HAVING A CYCLICALLY VARYINGMAGNETIC FIELD DEFINING A PARTICLE ORBIT AND A CYCLICALLY VARYINGELECTRICAL FIELD THEREAT FOR ACCELERATING IONS THEREAROUND, THE STEPSCOMPRISING GENERATING SAID IONS WITH A FIRST CHARGE-TO-MASS RATIO,ACCELERATING SAID IONS AT SAID ORBIT OF SAID SYNCHROTRON TO A FIRSTENERGY LEVEL DURING A FIRST CYCLE OF SAID MAGNETIC FIELD THEREOF,RAISING THE CHARGE-TO-MASS RATIO OF SAID IONS TO A SECOND HIGHER VALUE,AND FURTHER ACCELERATING SAID IONS AT SAID ORBIT IN SAID SYNCHROTON TO ASECOND HIGHER ENERGY LEVEL DURING A SUBSEQUENT CYCLE OF SAID MAGNETICFIELD, SAID FURTHER ACCELERATION OF SAID IONS BEING PHASED WITH A HIGHEHARMONIC OF SAID ELECTRICAL FIELD THAN THE INITIAL ACCELERATION THEREOF.